The present invention relates to a fluidized bed assembly with at least a first and a second fluidized bed chamber, each chamber having side walls and a bottom portion with means for introducing fluidization gas into the chamber. The present invention also relates to a fluidized bed cooler having walls defining an interior of a cooler chamber, and a bottom section with means for introducing fluidization gas into the cooler chamber. In such a cooler fine solid material is cooled in a fluidized state.
The invention also relates to a method of processing solid particulate material in a fluidized bed apparatus, such as a cooler, including at least two fluidization chambers, using a flow equalizer dividing the chambers, and extracting heat from the solid particulate in the fluidized bed.
There are several situations in fluidized bed reactors [such as circulating fluidized bed combustors or gasifiers, or even circulating fluidized bed gas coolers/solid preheaters] when a need arises for passing solid particulate material from one chamber to another, such as in cooling the circulating material to a certain level in a separate fluidized bed cooler. For example, when ash is being treated during discharging of the ash from the process and conveying it to a further processing location, it is necessary to set certain limits on the ash temperature; i.e., the ash must be cooled prior to its further handling. Such processing also minimizes heat loss from the assembly and increases reactor efficiency, by recovering heat.
U.S. Pat. No. 5,218,932 discloses a fluidized bed reactor and a method of operating it in which a bed of particulate material including fuel is formed in a furnace section. A stripper/cooler is located adjacent to the furnace section for receiving particulate material from the furnace section. The particulate material is first passed to the stripper section where air is supplied through the particulate material at a velocity sufficient to entrain relatively fine-grained portions of the particulate material. A plurality of spaced baffle members are disposed in the stripper section for acting on the entrained particulates to separate them from the air. The particulate material in the stripper section is passed to the cooler section in which air is passed through the particulate material at a velocity sufficient to cool the particulate material and entrain relatively fine-grained portions of the particulate material therewith. A second plurality of spaced baffle members is disposed in the cooler section for acting on the entrained particulates to separate them from the air. A drain pipe communicates with the cooler section for removing the particulate material from the reactor. The cooler section is divided into several sections by partition walls, the walls having openings at their opposite lower corners to enable the fluidized particulate material to move into the following section. This arrangement results in insufficient mixing of particulate material in the cooler section.
The article "Solids Flow Pattern and Heat Transfer in an Industrial-Scale Fluidized Bed Heat Exchanger" by Werdemann Cord, C. and Werther Joachim, Fluidized Bed Combustion, Vol. 2, ASME 1993, pp. 985-990, discloses a fluidized bed heat exchanger (FBHE) connected with a circulating fluidized bed (CFB) reactor. The FBHE is suggested to be formed by several chambers separated by solid partition walls. The movement of solids into successive chambers is designed to take place by overflow of the solids. This arrangement as well results in insufficient mixing of solids.
The article "Bed Ash Cooling and Removal Systems" by Modrak Thomas, M., Henschel Kay, J., Carmine Gagliardi, R. and Dicker John, M., Fluidized Bed Combustion, Vol. 2, ASME 1993, pp. 1325-1331 discloses a fluidized bed ash cooler (FBAC)in which the chamber is divided into sections with partition walls having an opening at their lower corners for solids to pass into the following section.
It has been discovered that the mixing of solids is insufficient in structures such as described above. Also, dead spaces or corners easily remain in such structure which hampers the heat transfer efficiency of the cooler resulting in unnecessary space and material consumption.
According to the present invention a method of and an apparatus for processing solid material in a fluidized bed apparatus are provided in which the above described drawbacks are eliminated, providing effective cooling of solids in association with a fluidized bed reactor.
In connection with this application the term "multiple solid flow" refers to a movement of fluidized solid material which approaches the movement of an equal flow velocity profile solid material in the movement direction.
According to a first aspect of the present invention a fluidized bed assembly is provided which comprises first and second fluidized bed chambers, each of the chambers having a bottom portion and side walls. Means are provided (such as a conventional grid, windbox, or the like) for introducing fluidizing gas into each of the bottom portions to fluidize particulates in the chamber. A flow equalizer separates the first and second chambers and provides a substantially uniform passage of particulates from the first chamber to the second chamber so that no dead spots or corners form in the chambers adjacent the flow equalizer.
Preferably at least one of the first and the second chambers includes heat transfer means immersed in the fluidized bed in the fluidized bed chamber and means for discharging gas from the fluidized bed chamber. Depending on the application only one or both of the first and second chambers may include heat transfer means. The heat transfer means may be, for example, evaporators, steam superheating or reheating devices, or feed water preheating or air preheating heat exchangers.
According to another aspect of the present invention the solid material flow equalizer comprises a barrier having at least two distinct openings spaced a predetermined distance from each other, the barrier providing preferably &lt;30% open area of the cross sectional area of the fluidized bed chambers at the barrier. Surprisingly, it has been discovered that a favorable result is obtained if the solid material flow equalizer comprises a wall or the like with at least two distinct openings spaced a distance from each other which is at its shortest 10-50% of the square root of the total area of the wall, and if the openings provide &lt;30% open area of the cross sectional area of the fluidized bed chambers. Optimization of openings may be obtained as follows: With the letter N referring to the number of distinct openings (N being an interger &gt;2), the distance between the openings is preferably defined to be between 1/N and 1/2 of the square root of the surface area of the wall.
According to yet another aspect of the present invention the solid material flow equalizer comprises a wall or the like with substantially evenly spaced openings. The wall may be a perforated wall with substantially evenly spaced openings. Preferably the openings are such that their largest diameter is &lt;50 mm.
Also, it has been noted to be favorable in some situations for the solid material flow equalizer to comprise a wall or like having a border zone with a width of 0.1 m at the periphery and openings in the wall.
The flow equalizer preferably comprises a barrier at the interface between the first and second chambers. The barrier has at least two openings associated therewith, preferably a plurality of substantially uniformly spaced openings, so that dead corners or spots are avoided. The barrier may be formed by a substantially continuous wall (generally planar in configuration) with through extending openings which may be perforations, quadrate in shape, or formed in a variety of other different forms. Alternatively the barrier may be formed by a number of obstacles which are independent from each other (or at least independent of some of the other obstacles) and mounted so that there are spaces between them, the spaces forming the openings. In either case heat exchange elements may be provided in the barrier for cooling particulates flowing through openings in the barrier.
According to yet another aspect of the present invention the fluidized bed apparatus may serve as a solid material cooler, wherein the cooling chambers or regions are separated from each other so that a chamber may be maintained at a certain temperature level substantially independently from other chambers. In practice this means that the adjacent fluidized beds are limited in their particle exchange at least backwards, i.e. at the border area of the zone chambers only unidirectional movement is desired, however, backflow to some extent is almost unavoidable. Excessive particle exchange is prevented, according to the present invention, by providing the solid equalizer (as described above) between the chambers, which equalizer preferably covers greater than 50% of the cross sectional area of said fluidized bed cooler at the border zone of the chambers.
The invention also comprises a fluidized bed assembly having first and second fluidized bed chambers, each chamber having a bottom portion and side walls, a means for introducing fluidizing gas into each of the bottom portions to fluidize particulates in the chambers. The assembly further comprises a barrier at the interface between the first and second elements, the barrier including at least two distinct openings spaced a distance from each other. That distance is, at its shortest, 10-50% of the square root of the area of the barrier, and the openings provide less than 30% open area at the cross sectional area at the interface between the first and second chambers.
According to yet another aspect of the present invention a method of processing solid particulate material in a fluidized bed including first and second fluidization chambers, and an interface therebetween, is provided. The method comprises the following steps: (a) Fluidizing solid particulate material in the first chamber. (b) Fluidizing solid particulate material in the second chamber. (c) Passing solid particulate material from the first chamber to the second chamber in at least two parallel distinct flows to substantially evenly introduce solid particulate material from the first chamber into the second chamber, so that there are no dead spots or corners adjacent the interface. And (d) uniformly mixing the distinct parallel flows of solid particulate material in the second chamber. Step (c) may be practiced by providing a flow equalizer barrier with at least two uniformly spaced openings between the first and second chambers. There is also preferably the further step of cooling the barrier to in turn cool solid particulate material passing through the openings, typically recovering heat from the solid particulate material.
It is the primary object of the present invention to provide effecting mixing of particulate materials during cooling in fluidized bed chambers, and uniform flow of particulate material from one chamber to another so that dead spots or corners are avoided. This and other objects of the invention will become clear from an inspection of the detailed description of the drawings and from the appended claims.